The present invention relates to a reader/writer and, more particularly, to a reader/writer which serves as, e.g., an information processing system to perform radio communication with a no-battery information storage medium such as a battery-less radio card or radio tag.
Recently, in the field of information processing apparatuses, information processing systems including an information processing apparatus such as a reader/writer for performing, in a noncontact state, radio communication with a no-battery information storage medium such as a battery-less radio card or radio tag applied as, e.g., an access control system has been developed.
In this case, while receiving the power by a radio wave transmitted from a transmission antenna on the information processing apparatus side such as the reader/writer, the no-battery information storage medium side such as the battery-less radio card or radio tag transmits data as an amplitude-modulated signal with a low degree of modulation to the reader/writer side.
The reader/writer side receives a radio wave transmitted from the battery-less radio card or radio tag side through a reception antenna.
The reader/writer side amplifies the received signal to a sufficient magnitude, and then performs detection processing and information processing for demodulating the received signal.
In this radio information processing system, however, communication between the reader/writer and the no-battery information storage medium such as the battery-less radio card or radio tag at a relatively short destance is influenced by the interference between the transmission and reception systems. The interference is due to the proximity of the transmission and reception antennas on the reader/writer side and results in inefficient transmission/reception.
In conventional signal processing where the amplitude-modulated signal with a low degree of modulation received on the reader/writer side is directly amplified to perform detection for modulation causes, saturation at a low power supply voltages, poses a problem in signal processing.